In a modern communications system, packet or frame transmission is a common communications manner. Packet transmission aims at correctly sending a packet from a source communication node to a destination communication node. However, packet loss occurs in an intermediate transmission process because of various reasons. Generally, there are mainly the following two reasons for a packet loss. The first reason is transmission congestion, that is, a packet sending requirement exceeds a packet transmission capacity of a network. If the packet sending requirement is not reduced, a packet that cannot be sent may be discarded. The second reason is a transmission error, that is, the transmission error occurs in a processing process of intermediate packet transmission. As a result, the destination communication node may not receive a correct packet. For example, an intermediate transmission line is interfered, and an error occurs in some bits of a packet. The transmission error is caused by various reasons and causes an error in a part or all of bits. Therefore, this type of error may be collectively referred to as a transmission bit error.
A packet loss may impair a communication service, and therefore, the packet loss needs to be reduced. An indicator for evaluating severity of the packet loss is a packet loss rate. A packet loss rate caused by transmission congestion may be decreased by reducing a packet transmission rate by means of flow control over a packet, but a packet loss rate caused by a transmission bit error cannot be reduced by flow control over a packet. Therefore, a reason for a current packet loss needs to be identified.
In the prior art, a packet loss rate is obtained according to the number of packets sent from a source node and the number of packets received by a destination node. When the packet loss rate is greater than a set threshold, it is determined that transmission congestion occurs. When the packet loss rate is less than a set threshold, it is determined that transmission congestion does not occur. However, in the foregoing method, a packet loss caused by a transmission bit error may be mistakenly determined as a packet loss caused by transmission congestion. As a result, packet loss determining is inaccurate, thereby causing incorrect flow control, extremely low utilization of transmission bandwidth, and even service interruption.